The present invention relates to a thyristor used with an associated circuit supplied with operating current from the thyristor, and more particularly to such a thyristor which has a shoulder of its n-base projecting through its p-base to the cathode side with a connection from the shoulder to an external circuit.
A thyristor of this general type is disclosed in German patent publication No. A-32 26 613. The associated circuit comprises a light-sensitive switch element connected between the conductive coating and the cathode of the thyristor. The switch element, such as for example a phototransistor, exhibits a relatively low blocking capability and a high photosensitivity, so that the overall system including the thyristor and the switch element comprises both a great trigger sensitivity as well as a great blocking capability. A disadvantage of this arrangement, however, is that the conductive coating, with a high blocking voltage, is close to the region of the space charge zone at the p-n junction between the two base layers, which space charge zone largely fills out the shoulder of the n-base. This leads to leakage currents which can bring about an unintentional ignition of the thyristor under some conditions, or which can make a desired ignition more difficult under other conditions.